1. Field of the Invention
The present invention relates to the production of thermal transfer sheets or ribbons, particularly donor transfer sheets of multiple, different colors laid down on a carrier layer by different processes, with different optical properties amongst the colors, or with combinations of normal and exotic colors. The process is particularly applicable for use in proofing, graphic arts (for the images themselves, for local area images (e.g., spot images) on top of other images), or animated film production, where large numbers of colors may be needed in a wide variety of volumes.
2. Background of the Art
The visual quality of a graphic arts spot color opaque image or an animated film is readily observable as a function of the quality and detail of the individual picture frames. The individual frames in the film of an animated production are photographic images taken of individual pictures of each individual frame. In the art of motion picture animation these individual pictures are called "cels". A "cel" may consist of several sub-cels, each of separate image areas. In the highest quality cels, the background area (sub cel) is drawn, usually by hand, and hand painted overlays of the active characters are placed over the background areas in overlaid sub-cels and the composite scene photographed. The active character Figures are progressively different (and individually painted that way) for each cel. This is an exceedingly expensive procedure when the highest quality images are desired.
In lower quality animated films, such as those often produced expressly for low budget television, expenses are reduced by reducing the degree of activity of the characters. With lower levels of activity, the background area can encompass greater proportions of the active character, with less of the character having to be drawn to show its movement. For example, the background could include the normal scenic background and all of the character except for its mouth. The only overlay for the cel would have to be the moving lower jaw of the character to show that it was speaking.
Modern animated films can now use computer driven imaging systems to create the cels. The cells may be hand drawn and scanned, drawn on a digital screen and converted to digital data for the computer, and the data may be enhanced by computer programs. Various programs are available where the computer can create the data of intermediate images between two scenes by a process called `morphization,` where given a beginning position and an end position for a Figure, the computer will generate the intermediate frames without the need for hand drawing. Any system which is capable of being data driven by a computer may be used as the image output system to produce the actual cels, but color negative photographic imaging provides the highest quality images for the motion picture industry. This is still an expensive procedure and does not provide a wide range of flexibility in the production of the cel.
There are also specific properties in the image of the cel which limit the types of imaging systems which could be useful in the manufacture of cels. For example, specific image areas in the overlays must be opaque so that the background does not show through the overlay. The traditional process for making animation cells is shown in U.S. Pat. No. 2,351,634 (W. Disney) and British Patents 595,255 (W. Disney) and 531,094 (R. Place). Opaque, hand-applied paints are used for each feature in the overlay of the cels.
Once the image and background cels are overlaid, they are photographed onto color negative photographic film. One frame of photographic film is exposed for each final frame image needed in the final film, which may be as many as hundreds of thousands of frames for a full length animated movie.
One other method which has been used to reduce the labor intensive steps in the animated film making process includes electronic printing. In that manner image assembly is combined with integral opaquing (that is opaquing steps that are an integral part of electronic imaging).
Each color which is used in the formation of the cels adds additional expense. The number of colors used in the animation is such a large factor in the cost of a production, that it is a part of the animated film making process to assign one individual, the Color Model Advisor, to analyze the animators' drawings for excessive detail, particularly with respect to excessive numbers of colors. As an example of this process, it is said that Jiminy Cricket had as many as twenty-seven colors in the Walt Disney animated film version of Pinocchio. When that same character was used on the Walt Disney Mickey Mouse Club films, the number of colors used was only nine. This was a very significant cost savings. Even the simplest characters will have at least about nine colors, so the cost of the production is greater with significant artistic enhancement of the character image, which would require many more colors.
Additional expenses are incurred in putting any color background or character on the screen. To begin with, each color utilized in an image represents an expense in itself. Each artist must have access to custom made bottles of ink with at least twice that quantity of colors estimated to be necessary for the full production requirements to insure production color quality control. The actual steps involved in cel production include paint mixing (and color control of the mixed paint), packaging and dispensing (to the various individual painters), precision "cel" area painting and drying times. All these times are additive for each color. Bottled color ink inventory control and remixture, when use exceeds inventory, causes color changes that waste time. Time can be reduced somewhat by means of computer directed dry color imaging and opaquing.
Eventually, the individual color or composite "cels" have to be photographed onto a color photographic media which has the capability of producing over 1.6 billion colors. The limited color gamut imposed by hand color ink mixing and "cel" inking restrict the final quality of the production. The special effects art and design techniques are even more labor intensive. The advent of the computer tended to eliminate some of the mechanical drudgery, but cel production still used labor intensive means.
Yet another labor intensive, but traditional animation operation, is "a self ink line". To keep the color within the image outline, each separate color must have an outline around it defining its border to the area next to it. In a particular Figure, the hat is one color, the hair another, etc. When these outlines are done using black ink, there is a heavy, crude look that is fine for some characters, but unacceptable for more delicate ones. Colored inks were tried and were an improvement, but when a look of quality and careful shading was needed, they were still too strong. Presently, lines may be inked on the back of the cel. The paint used is diluted to soften it. The combination of the diffusion effect and the diluted ink allows better colored image outline scarcely noticed on the screen. This technique provides soft color changes, delicate shades, and subdued values.
Additionally, the fully painted "cel" itself can represent a problem, the solution of which complicates production time and expense. Looking at a composite "cel" of Snow White, Disney's artists felt that the black hair looked unnatural and harsh, They added a wisp of drybrush in a lighter grey to soften the edge of her hair. It helped immensely, so they proceeded to add it to every cel all through the picture. This had to be done on top of the cels, and the only way to be sure the effect was working from one to the next was by flipping the whole sheet of celluloid, heavy with paint. The task was effective but it was tiring and risked cracking the paint. This risk is still taken on important productions.
The means of production and subsequent reproduction of each cel in a single frame of, and in a complete motion picture has been detailed in U.S. Pat. No. 2,281,033 by Garity assigned to W. Disney as well as Disney Animation, the Illusion Of Life by F. Thomas and O. Johnston, Abbeville Press, N.Y. 1981 pages 47-71, "The Principles of Animation"; and "How to Get it on Screen" pages 243-285. Such techniques are as efficient with respect to today's technologies as is the use of room filled mainframe computers is to desk top imaging systems.
The use of thermal transfer systems would significantly help in the reduction of costs, but the need for a large number of different and unusual colors from those ordinarily in production would tend to maintain a higher level of cost than is desired. It is therefore important to provide a process for readily manufacturing thermal transfer donor materials of a variety of tailored colors at a lower cost than can be done by present manufacturing techniques for thermal transfer donor materials.
Donor sheets, film or ribbon elements which may be heated on one surface to transfer colorant (dye, pigment, pigment in a binder) to a receptor surface are used in thermal imaging processes. Donor sheets are typically made by a single type of process for applying each and every colorant to the donor sheet substrate.